Since the advent of electrospray (which is extensively described by U.S. Pat. Nos. 4,531,056 and 4,542,293), Electrospray (ES) and Atmospheric Pressure Chemical Ionization (APCI) source designs have evolved. Descriptions of ion sources which operate at atmospheric pressure, such as ES and APCI interfaced to mass analyzer systems, are found in U.S. Pat. Nos. 5,581,080; 5,432,343; 5,157,260; 5,130,538; 5,015,845; 4,999,493; 4,977,320; 4,209,696; 4,144,451; 4,137,750; 4,121,099; and 4,023,398 (the disclosures of which are incorporated herein by reference). Earlier ES and APCI sources were designed to maximize analytical performance with less regard for the convenience and ease of cleaning and maintenance as the main design criteria. Later, commercially available API sources from mass spectrometer (MS) manufacturers, including Perkin-Elmer Sciex and Finnigan, were designed for increased user convenience in maintenance of API sources. These API mass spectrometer systems which include two to three vacuum stages have assemblies that plug into the front of the instrument or swing open via a hinged joint. These commercially available removable assemblies include no more than two vacuum partitions and the ion guide assemblies included in these instruments are only removable as separate assemblies. However, these assemblies which include an ion optics transfer assembly with one or two vacuum pumping stage partitions, only allow access to the first vacuum stage or second vacuum stage and do not allow easy access to deeper vacuum stages or other ion optics without completely removing additional assemblies from the mass spectrometer. These commercially available removable assemblies include an orifice or a capillary into vacuum, as well as a skimmer, but do not include multipole ion guide(s) in the same removable assemblies.
The ability to interface to liquid introduction systems has greatly broadened the appeal of mass spectrometry as an analytical technique. As a direct consequence of this appeal, substantial resources have been invested and significant costs incurred by end-users for the operation and maintenance of mass spectrometric instrumentation, thereby placing an increased premium on instrument ruggedness, robustness and operability. At the same time, the diversity of backgrounds of all of the possible end-users of this technology all but prohibits having an expert in mass spectrometric hardware design continually on-site and available for complex instrument maintenance. The present inventors have recognized and addressed the current problems in the prior art by development of the present invention, which makes the optimal practice of API-MS more accessible.